Retinal prosthesis with multiple electrode arrays for greater field of view

ABSTRACT

The artificial percept of light may be created by electrically stimulating the neurons of the retina. While a photolithographed array internal to the retina provides superior resolution, an array external to the retina provides easier implantation and improved manufacturability. Therefore it is advantageous to supply a high-resolution electrode array internal to the sclera, near the fovea and a lower-resolution electrode array eternal to the sclera near the periphery of the retina. 
     It is advantageous to encourage current to flow through the retina by providing a physically separate and distinct electrode array and return electrode. The high-resolution electrode array and lower-resolution electrode array may be return electrodes for the other, or completely separate return electrodes may be provided.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/227,132, filed Sep. 7, 2011, entitled Retinal Prosthesis withSeparate Electrode Array and Return Electrodes, which is a continuationapplication of U.S. patent application Ser. No. 11/924,458, filed Oct.25, 2007, entitled Retinal Prosthesis with Separate Central ElectrodeArray and Peripheral Electrode Array, now U.S. Pat. No. 8,036,752 whichis a continuation application of U.S. patent application Ser. No.11/418,677, filed May 4, 2006, entitled Retinal Prosthesis with SeparateCentral Electrode Array and Peripheral Electrode Array, now U.S. Pat.No. 7,904,163, which claims the benefit of U.S. Provisional ApplicationNo. 60/677,551, 2005 entitled Retinal Prosthesis with Internal CentralElectrodes and External Peripheral Electrodes, filed May 4, 2005, whichare hereby incorporated by reference.

This application is related to U.S. patent application Ser. No.09/783,236 filed Feb. 13, 2001, entitled Implantable Retinal ElectrodeArray Configuration for Minimal Retinal Damage and Method of ReducingRetinal Stress, now U.S. Pat. No. 7,338,522, and U.S. patent applicationSer. No. 10/112,801, filed Mar. 28, 2002, entitled Variable PitchElectrode Array, now U.S. Pat. No. 7,149,586, and U.S. patentapplication Ser. No. 11/413,689, filed Apr. 28, 2006, now U.S. Pat. No.8,639,344, entitled Flexible Circuit Electrode Array, which are herebyincorporated herein by reference.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support under grant No.R24EY12893-01, awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention is generally directed to a visual prosthesis andmore specifically to an improved mechanical and electrical configurationfor retinal prosthesis for artificial vision.

BACKGROUND OF THE INVENTION

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising a prosthesis foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparati to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases such as retinitis pigmentosaand age related macular degeneration which affect millions of peopleworldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the information as a sequence of electricalpulses which are relayed to the nervous system via the prostheticdevice. In this way, it is possible to provide artificial sensationsincluding vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretinal). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, and avoid undue compression of thevisual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 uAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNormann describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Humayun, U.S. Pat. No.5,935,155 describes the use of retinal tacks to attach a retinal arrayto the retina. Alternatively, an electrode array may be attached bymagnets or glue. U.S. Pat. No. 5,109,844 to de Juan describes a flatelectrode array placed against the retina for visual stimulation.

A human retina naturally provides very high-resolution near the fovea atthe center of vision. Resolution near the periphery is much lower and isprimarily designed to detect movement. When our peripheral visiondetects movement, we move first our eyes, and then our heads toward themovement, detecting the object with our fovea. This happens so quicklyand automatically, that we are generally unaware of the lower resolutionin the periphery. Further, we tend to scan a scene and our brainremembers details after they are scanned by the fovea. This gives us theperception of continuous high-resolution vision.

Photolithographic techniques are the best know technique for creating anelectrode array that approaches the natural resolution of the fovea.However, photolithographic techniques require that the array be madeflat, not curved like the retina. Other techniques such a siliconemolding over hand welded wires are easily made curved, but can notproduce the high-resolution of a photolithographic array.

Further, it is necessary to implant electronic drivers for theelectrodes external to the eye as the vitreous within the eye will notefficiently dissipate the heat of the electronics. It is difficult topass a large number of wires through the sclera because the incision, orscleratomy, much heal and seal around those wires.

SUMMARY OF THE INVENTION

The artificial percept of light may be created by electricallystimulating the neurons of the retina. While a photolithographed arrayinternal to the retina provides superior resolution, an array externalto the retina provides easier implantation and improvedmanufacturability. Therefore it is advantageous to supply ahigh-resolution electrode array internal to the sclera, near the foveaand a lower-resolution electrode array eternal to the sclera near theperiphery of the retina.

The preferred method of manufacturing a high-resolution electrode arrayis through photolithography, which requires the array to be made flat.While it is possible to curve the array afterward, it is difficult andcostly. I small high-resolution array can be implanted near the fovea.Due to its small size, curvature is less of an issue. A largerlower-resolution array can be molded in silicone or similar method andplaced around the periphery, of the retina, where the retina isnaturally lower-resolution. Further, the lower-resolution array can beimplanted external to the sclera reducing the number of electricalconnectors passing through the sclera.

Even if a separate lower-resolution array is implanted internal to thesclera, super-choroidal (between the choroid and sclera) orintra-scleral (between the layers of the sclera), it is easier to make alower-resolution array in a curved shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the implanted portion of the preferredretinal prosthesis.

FIG. 2 is a side view of the implanted portion of the preferred retinalprosthesis showing the fan tail in more detail.

FIG. 3 is a perspective view of an alternate embodiment of the implantedportion of a retinal prosthesis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

FIG. 1 shows a perspective view of the implanted portion of thepreferred retinal prosthesis. A high-resolution electrode array 10 ismounted by a retinal tack or similar means to the epiretinal surfacenear the fovea. The high-resolution electrode array 10 is electricallycoupled by a cable 12, which pierces the sclera and is electricallycoupled to an electronics package 14, external to the sclera.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil may be madefrom a thin film polymer sandwich with wire traces deposited betweenlayers of thin film polymer. The electronics package 14 and secondaryinductive coil 16 are held together by a molded body 18. The molded body18 may also include suture tabs 20. The molded body narrows to form astrap 22, which surrounds the sclera and holds the molded body 18,secondary inductive coil 16, and electronics package 14 in place. Thestrap 22 further supports a lower-resolution electrode array 30, mountedexternal to the sclera. The lower-resolution electrode array 30surrounds the peripheral retina and supports electrodes for stimulatingpercepts in the periphery of the retina. The external electrode array ispreferable molded of silicone in a curved shape and highly flexible. Themolded body 18, suture tabs 20 strap 22 and lower-resolution electrodearray 30 are preferably an integrated unit made of silicone elastomer.Silicone elastomer can be formed in a pre-curved shape to match thecurvature of a typical sclera. However, silicone remains flexible enoughto accommodate implantation and to adapt to variations in the curvatureand size of an individual sclera. The secondary inductive coil 16 andmolded body 18 are preferably oval shaped. A strap can better support anoval shaped coil.

The lower-resolution array 30 may be integrally molded into the strap 22or a separate structure, which passes under the strap 22. Thelower-resolution electrode array 30 may extend both in front of thestrap to the pars plana and behind the strap to cover all of the retinaleaving a gap 32 over that portion of the retina stimulated by thehigh-resolution electrode array and the optic nerve. Ideally, thelower-resolution electrode array extends beyond the portion of the strap22 that passes through the buckle 23, to provide full 360° stimulation.The lower-resolution electrode array 30 may overlap itself toaccommodate different size scleras. After implantation, overlappingelectrodes may be disabled. Particularly, if the lower-resolutionelectrode array 30 is separate from the strap 22, it would beadvantageous to provide suture tabs 34 directly on the lower-resolutionelectrode array 30.

It should be noted that the entire implant is attached to and supportedby the sclera. An eye moves constantly. The eye moves to scan a sceneand also has a jitter motion to improve acuity. Even though such motionis useless in the blind, it often continues long after a person has losttheir sight. It is an advantage of the present design, that the entireimplanted portion of the prosthesis is attached to and supported by thesclera. The lower-resolution electrode array 30, though mountedexternally, must move with the retina to give a consistent visual image.Also, by placing the device under the rectus muscles with theelectronics package in an area of fatty issue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

It is further advantageous to provide a remote return or commonelectrode for each electrode array on the opposite side of the retinafrom the electrode array, thereby causing current to flow through theretina. For the high-resolution array 10, the outer case of theelectronics package 14 provides a remote return electrode. For thelower-resolution electrode array 30, remote return electrode 36 may beplaced internal to the eye. Alternatively, the lower-resolutionelectrode array 30 may provide the remote return electrode for thehigh-resolution array 10, and the high-resolution array 10 may providethe remote return electrode for the lower-resolution array 30.

FIG. 2 shows a side view of the implanted portion of the retinalprosthesis, in particular, emphasizing the fan-tail 24 and the shape ofthe lower-resolution electrode array 30. When implanting the retinalprosthesis, it is necessary to pass the strap 22 and lower-resolutionelectrode array 30 under the eye muscles to surround the sclera. Thesecondary inductive coil 16 and molded body 18 must also follow thestrap under the lateral rectus muscle on the side of the sclera. Theimplanted portion of the retinal prosthesis is very delicate. It is easyto tear the molded body 18 or break wires in the secondary inductivecoil 16. In order to allow the molded body 18 to slide smoothly underthe lateral rectus muscle, the molded body is shaped in the form of afan tail 24 on the end opposite the electronics package 14.

Reinforced attachment points 26 are provided to facilitate handling ofthe retinal prosthesis by surgical tools. Preferably, the reinforcedattachment points are harder silicone formed around holes through themolded body 18. Further, a hook 28 is molded into the strap 22 justbeyond the end of the fan tail 24. A surgical tool can be used againstthe hook 28 to push the strap 22 under the rectus muscles. The hook 28is more clearly depicted by the edge view of FIG. 3. The strap 22 isattached to itself by a sleeve 23. The sleeve 23 is a friction devicethat connects two silicone bands and holds them together with friction.The sleeve 23 is similar to a Watzke sleeve, used with a scleral buckle,and is well known in the art.

In the preferred embodiment, the high-resolution electrode array 10 andcable 12 are formed layers of a thin polymer film with metal tracessandwiched between the thin polymer films. In such an embodiment, it isadvantageous that the film with openings for high-resolution electrodearray 10 be the same film with an opening for connection to theelectronics package 14. Therefore, the cable 12 exits the electronicspackage up away from the fantail 24, folds over itself and exits downtoward the fantail 24, before turning at a right angle and piercing thesclera. This allows the same side of the cable to face both theelectronics package and the retina. The cable 12 may also include afantail at the point it is attached to the electronics package 14 and atthe point it is attached to the high-resolution electrode array 10 toreduce any stress on the connections that may be caused by implantation.It is important that the cable exit the molded body 18 toward the frontof the eye. The cable must travel above the lateral rectus muscle andpierce the sclera at the pars plana, in front of the retina, so it doesnot damage the retina. Once inside the eye, the cable 12 can fold backover the retina to properly locate the high-resolution electrode array10 on the epiretinal surface.

Fundamentally, the lower the resolution of the array, the easier it isto form the array to shape of the retina. While described here as twoarrays, one higher resolution and less flexible, and onelower-resolution and more flexible, it possible to use more than twoarrays using more than two array technologies. Its is also possible touse the same array technology and tile segments to achieve a rounderoverall shape. With thin film technology curving the array, afterdeposition of the metal traces can cause the traces to break. Hence, theprosthesis may provide a high-resolution array, a middle resolutionarray and a lower-resolution array or even more variations.

It may be advantageous to use two thin film arrays, a small higherresolution array with very thin metal traces and a lower-resolution thinfilm array with more curvature and more robust metal traces.

The lower resolution electrode array may be a photolithographically-madethin film array. While it is difficult to curve a thin film in twodimensions to follow the spherical shape of the retina, it is easy tocurve a thin film in one dimension, such as a cylinder. Hence, a thinfilm can be used to make a generally cylindrical array around theperiphery of the retina, either externally or internally to the retina.

Alternatively, as shown in FIG. 3, the lower-resolution array 130 may betiled small sections of thin film arrays. A high-resolution electrodearray 110 is mounted by a retinal tack or similar means to theepiretinal surface near the fovea. The high-resolution electrode array110 is electrically coupled by a cable 112, which pierces the sclera andis electrically coupled to an electronics package 114, external to thesclera.

The electronics package 114 is electrically coupled to a secondaryinductive coil 16. The electronics package 114 and secondary inductivecoil 116 are held together by a molded body 18. The molded body 118 mayalso include suture tabs 120. The molded body narrows to form a strap122, which surrounds the sclera and holds the molded body 118, secondaryinductive coil 116, and electronics package 114 in place. The strap 122further supports a lower-resolution electrode array 130, mountedexternal to the sclera. The lower-resolution electrode array 130surrounds the peripheral retina and supports electrodes for stimulatingpercepts in the periphery of the retina. The lower-resolution electrodearray is preferable tiled sections of thin film array, which aresufficiently small that they conform to the curvature of the retina. Thelower-resolution electrode array 130 may extend both in front of thestrap to the pars plana and behind the strap to cover the entire retinaleaving a gap 132 over that portion of the retina stimulated by thehigh-resolution electrode array and the optic nerve. Ideally, thelower-resolution electrode array extends beyond the portion of the strap122 that passes through the buckle 123, to provide full 360°stimulation. The lower-resolution electrode array 130 may overlap itselfto accommodate different size scleras. After implantation, overlappingelectrodes may be disabled. Particularly, if the lower-resolutionelectrode array 130 is separate from the strap 122, it would beadvantageous to provide suture tabs 134 directly on the lower-resolutionelectrode array 130.

While the preferred embodiment provides for the lower-resolution arrayto be external to the sclera, it is advantageous to provide multiplearrays of different technologies even if they are all implanted on theepi-retinal surface. It is also possible to provide differingimplantation methods for different array types. Options for implantationinclude epi-retinal, sub-retinal, super-choroidal, intra-scleral andextra-scleral. Epi-retinal is on the inner retinal surface in thevitreous humor. Sub-retinal is on the outer retinal surface between theretina and the choroid. Super-choroidal is between the choroid andsclera. Intra-scleral in within the layers of the sclera. Extra-scleralis outside the sclera. Each implantation location provides uniqueadvantages and disadvantages. It should be clear to one of skill in theart that the array technologies and array placements may be combined inmany permutations to achieve any desired result.

Accordingly, what has been shown is an improved retinal prosthesis.While the invention has been described by means of specific embodimentsand applications thereof, it is understood that numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is therefore tobe understood that within the scope of the claims, the invention may bepracticed otherwise than as specifically described herein.

The invention claimed is:
 1. A retinal prosthesis comprising: a firstelectrode array being made of a thin film sandwich, adapted to supportclosely spaced smaller electrodes and to be placed close to the fovea ofan eye; a second electrode array physically distinct and separate fromthe first electrode array suitable to be mounted to an eye further fromthe fovea than the first electrode array, the second electrode arraybeing made of molded polymer to support larger more widely spacedelectrodes and being larger and more curved than the first electrodearray; an electronics package suitable to be mounted external to asclera, the electronics package electrically coupled to the firstelectrode array and the second electrode array.
 2. The retinalprosthesis according to claim 1, further comprising a secondaryinductive coil electrically coupled to the electronics package andsuitable to be mounted to the side of the sclera.
 3. The retinalprosthesis according to claim 2, further comprising a strap connected tothe secondary inductive coil and surrounding the sclera.
 4. The retinalprosthesis according to claim 3, wherein the strap supports theelectronics package.
 5. The retinal prosthesis according to claim 3,wherein the strap supports the second electrode array.
 6. The retinalprosthesis according to claim 2, further comprising suture tabsconnected to the secondary inductive coil suitable for attaching thesecondary inductive coil to a sclera.
 7. The retinal prosthesisaccording to claim 1, wherein the first electrode array is suitable tobe mounted internal to the sclera and the second electrode array issuitable to be mounted external to the sclera.
 8. The retinal prosthesisaccording to claim 1, wherein the first electrode array and a cableconnecting the first electrode array to the electronics packages are aflexible circuit of metal traces between polymer films.
 9. The retinalprosthesis according to claim 8, wherein the flexible circuit issuitable to pierce pars plana region of the sclera.
 10. The retinalprosthesis according to claim 1, wherein the first electrode array issuitable to be placed in an epiretinal location.